A hinge assembly is conventionally used to support a door on the body structure of a vehicle. Generally, such a hinge assembly includes a pair of pivotally connected hinge members or straps, a stationary hinge strap secured to the body structure and a movable hinge strap secured to the vehicle door. Often, the hinge assembly includes a hold open means designed to releasably hold the movable hinge member, and thus the vehicle door, in a plurality of discrete hold open positions. Generally, the hold open positions number two. A typical hold open means includes a detent link pivotally supported on the movable hinge strap. A relatively strong spring operatively connected to the detent link biases it toward a cam means supported on the stationary hinge strap. The cam means includes a cam roller that turns on the end of a stop pin fixed to the stationary hinge strap. The detent link includes an edge having a pair of spaced apart arcuate surfaces that define first and second detent notches.
As an operator opens the door from closed position, the spring keeps the edge of the pivoted detent link resiliently biased into the cam roller. The cam roller rolls along the edge of the detent link and forces the detent link about its pivot against the force of the spring. As the door continues to open, the cam roller rolls into the first detent notch, and the spring expands as the detent link moves back about its pivot. The force of the spring maintains the cam roller in the first detent notch, thereby releasably holding the movable hinge strap and the door in a first hold open position. As the operator opens the door further, the cam roller rolls out of the first detent notch, and again forces the detent link about its pivot against the force of the spring. The cam roller then rolls into the second detent notch, to similarly hold the movable hinge strap and door in a second hold open position. As the operator pulls the door back to the closed position, these motions of cam roller and detent link are reversed.
The spring used must necessarily be quite strong, especially in the case of a large and heavy door. Consequently, the force with which the cam roller rolls into the detent notch may be considerable. In addition, the angular interval covered by the door and hinge members between the hold open positions is not large, generally on the order of 20 degrees. Therefore, the movement of the detent link about its pivot as the cam roller rolls out of one detent notch and into another, and the simultaneous compression and expansion of the strong spring, may occur quite rapidly. Further, other portions of the detent link edge on which the cam roller rolls may be steeply sloped, especially the portion engaged as the door approaches its closed position. Again, because of the strong spring, the roller may be forced rapidly along those other portions of the detent link edge. These rapid and forceful motions of the detent link can cause a rough motion of the hinge member to which it is supported, and a consequent rough feel as perceived by the operator of the door.